The invention relates to a balance with a housing that accommodates the weighing mechanism and the weighing electronics. The housing has at least three positioning feet to stand on a supporting surface, with at least two of the positioning feet being height-adjustable so that the balance can be set up in a level position.
Balances of the kind encompassed by the invention are used primarily in laboratories, production facilities and stock rooms and are distinguished in particular by a weighing pan with a large surface area. They often have three positioning feet to stand on, which are arranged at the corners of an isosceles triangle. This kind of support presents the problem that the balance is easily destabilized when a load is placed eccentrically on the weighing pan, or under any other off-center force, i.e. under a vertical force that is applied outside of the tipping boundary. In this condition, the balance no longer stands on its three positioning feet and is therefore no longer in the correct reference position.
The known state of the art includes balances such as the PR model series by the Swiss company Mettler-Toledo GmbH, that have three positioning feet resting on a supporting surface, where two of the positioning feet that are located near the corners at the front of the balance are height-adjustable by means of a screw arrangement. The adjustable feet serve to set the balance into a level position or, stated more precisely, into the reference position in which the weighing accuracy of the balance was adjusted. A third positioning foot is arranged midway, i.e., in a place on the centerline at the bottom of the balance near the rear end of the balance. This balance, particularly in model versions with a large-area weighing pan, is equipped with two additional feet, referred to as stabilizer feet. After the balance has been level-adjusted, the stabilizer feet are backed out far enough from their screw threads in the bottom of the balance housing until they are in firm contact with the supporting surface on which the balance rests, so that the balance is supported also at the two rear corners. Consequently, the balance cannot tip over even under loads that are placed off the centerline in the rearward portion of the weighing pan.
The foregoing concept of screw-adjustable stabilizer feet has the disadvantage that the point where the stabilizer feet come into contact with the supporting surface cannot be exactly determined, which entails the risk that the stabilizer feet are turned out too far so that at least one of the positioning feet is raised slightly from the supporting surface, which puts the balance again out of its reference position. Furthermore, it is not immediately and clearly evident to the user, in which direction he needs to turn the screw-adjustable stabilizer foot.
A balance that is disclosed in JP 10 048 035 A has two positioning feet that are height-adjustable to put the balance into a leveled position and are located near the corners at the front of the balance housing where an indicating- and operating unit is arranged. At the rear of the balance housing, a lever extending over nearly the entire width of the balance is attached to a fulcrum on the centerline of the balance and has a stabilizer foot at each end. The lever can be locked in position at its fulcrum on the balance housing, or it can be released to allow a rotation about the fulcrum point. The preferred means for locking and releasing the lever is a screw which in its tightened condition clamps the lever against the balance housing. The balance is leveled in the released condition of the lever where the balance always rests on all four feet. After the balance has been level-adjusted to its correct reference position, the lever is locked, whereby the stability of the reference position is secured as the balance in its operating state continues to rest on four feet.
This balance suffers from the drawback that the locking of the lever is accomplished by means of a screw, which creates the risk that at the instant of locking, a torque can be exerted on the lever, which could possibly put the balance out of its reference position again. In addition, the arrangement of the foregoing description is extremely sensitive to vibrations, especially if the lever is not designed to be particularly rigid. To design the lever with adequate rigidity would, however, require more space.